1. Field of the Invention
The present invention relates to a method for rollover detection for automotive vehicles with safety-related devices, in which the angular velocity of rolling or rotary motions around the longitudinal axis (roll-axis) of the vehicle is measured by means of a gyrosensor.
2. Description of the Related Technology
A method for rollover detection is known from DE 196 09 717 A1, in which, in each case an angular rate sensor measures the angular velocity around the vertical axis (yaw axis), the longitudinal axis and the transverse axis (pitch axis) of the vehicle, and detects a rollover when at least one of the measured angular velocities exceeds a defined threshold value (limiting value) Furthermore, this publication proposes calculating the rotational energy of the vehicle from the angular velocities, and indicating an impending rollover when the rotational energy exceeds a defined threshold. However, the disadvantage of this method is that false decisions cannot be excluded, when for example the vehicle is traveling over steep terrain, is subject to slow rolling motions while traveling around curves or fast rolling motions, especially when entering steep curves.
In order to avoid such false decisions in the rollover detection, in DE 197 44 084 it is proposed to determine the initial position, that is the starting position of the vehicle, by measuring the accelerations of the vehicle in the directions of its vertical axis (yaw axis), longitudinal axis and transverse axis (pitch axis) in order to be able to calculate from them the initial position angle, that is the starting position angle. This initial position angle is used as an integration constant for integrating measured angular rates, for example around the longitudinal axis, to determine the current position angle of the vehicle. The implementation of this known method is expensive because it requires a large number of sensorsxe2x80x94three acceleration sensors and at least one angular rate sensor. Apart from that, the reliability of this method needs improvement because the threshold value cannot be specified in such a manner that all the rollover scenarios which occur (that is fast and slow rollovers, driving through a steep curve or driving along a screw ramp with a subsequent rollover) are detected with certainty and reliability.
A method for detecting a rollover in which only one inclination sensor and one angular rate sensor are used is known from WO99/50103. In this known method, a safety-related device is triggered when both the signal from the angular rate sensor and the signal from the inclination sensor exceed their defined threshold values. Because only the angular velocity, taking into consideration the angular position of the vehicle, is used for detecting a rollover, only fast rollovers can be detected in good time with this arrangement, not however, slow, so-called quasi-static rollovers.
Finally, a safety system for automotive vehicles with an electronic arrangement for controlling at least one safety-related device in case of an automotive vehicle rollover is known from EP 0,430,813 B1. This safety system contains a gyrometer (angular rate sensor or gyrosensor) which measures the rotational velocity of the rolling motion, and accelerometers for measuring the acceleration values in the directions of the vertical, longitudinal and transverse axes in order to calculate from them a value proportional to the inclination angle in the transverse direction, etc. When a threshold value is exceeded by this last-mentioned value, the signals coming from the gyrometer and from the acceleration sensors are evaluated by the electronics arrangement which controls the triggering of the safety-related device by integrating the angular rate signal during a defined time window. This simply prevents the integration from overflowing.
The primary disadvantage of the triggering algorithm used in the above known safety system is that, as well as the signals of the angular rate sensor, other signals are required to prevent the integration from overflowing, namely signals from acceleration sensors which simply serve the purpose of enabling the angular rate sensor signals to be evaluated, but which result in high manufacturing costs for the overall system. A further known disadvantage is that the evaluation of the angular rate signal does not take into consideration the automotive vehicle position, that is the starting position angle in relation to the horizontal plane.
The object of the present invention is to provide a method for detecting rollovers in automotive vehicles which avoids the above-mentioned disadvantages, that is, it can be implemented economically, but is nevertheless highly reliable, both in respect of detecting a rollover in good time as well as in excluding false triggering.
According to the present invention, this object is achieved such that, starting from the position angle indicating the initial position of the vehicle, the integrated angular rate signalxe2x80x94as an angle of rotationxe2x80x94is added so that the amount of this value proportional to the momentary inclination angle (in relation to the horizontal plane) can be compared with a trigger threshold which is a function of the angular rate. If this trigger threshold is exceeded by the summation value, then a safety-related device is triggered, for example a roll bar, seat-belt tensioners and possibly a plurality of airbags.
In an advantageous embodiment of the method according to the invention, additional dynamic motion variables of the vehicle are recorded, these may preferably be accelerations in the directions of the vertical axis, the transverse axis and the inclination in relation to the horizontal position in the transverse direction, and their plausibility, that is their self-consistency, is evaluated. If these values are intrinsically self-consistent, from the acceleration values, the current inclination angle or, if the sensor generating the initial position signal is used as an inclination sensor, its value as a current inclination angle is used as the starting variable of the integration of the angular rate signal and the integral is reset to zero at the same time. However, if these values are not assessed as self-consistent, then the calculated inclination angle is reduced to an assessed value, and this assessed value is used as the starting variable of the integration of the angular rate signal, in which, here again, the integral is reset to zero before this assessed value is taken over.
With an integration of the angular rate performed over a longer period, errors and deviations from the actual angle of rotation are taken into account and avoided, so that the reliability of the method is further increased.
The value zero is preferably taken as the assessed value for the current inclination angle, or the value of the last inclination angle determined from the dynamic motion variables which was assessed as being self-consistent is used. In this regard, the calculated current inclination angle can be returned in stages to the assessed value in successive time segments, or this can take place continuously over a defined time segment.
This return eliminates several sources of error. So, on the one hand, the drift velocity (i.e. the stability of the quiescent value) of the gyrosensor is taken into account by selecting the time segments according to the magnitude of this drift velocity, preferably in the order of minutes, and, on the other hand, inertial forces resulting from dynamic processes may falsify the values of sensors which indicate the level of a fluid, and thus respond correspondingly slowly, or lead to a xe2x80x9cspill overxe2x80x9d in the case of short and sharp accelerations in their direction of sensitivity, or as acceleration sensors measured values generated under fast motions (for example in the Z- and Y-directions) do not permit a sufficiently exact calculation of an inclination because of the occurring inertial forces. Finally, when driven along a bumpy track, the minor inclination fluctuations which occur must be prevented from being integrated to form a critical value. The plausibility test only accepts a measured value as a value proportional to the inclination angle if all the sensors"" measured values are in defined, self-consistent relations to one another.
Preferably, the vertical acceleration az and, if applicable, the lateral acceleration ay can also be measured as additional dynamic motion variablesxe2x80x94if the inclination is to be calculated from themxe2x80x94as well as the value for the inclination angle xcex1 supplied by the initial position sensor (more precisely: the value proportional to this). The az and ay values supplied by the acceleration sensors and the xcex1 values generated by this inclination sensor, or the values calculated for the current inclination angle on the basis of the az and ay values are tested for plausibility, i.e. for self-consistency. The advantage of these measures is that more accurate information about the current inclination angle can be generated, which then forms the integration constant for the angular rate signal which significantly increases the reliability.